I built an O2 Amp and it works fine sometime and sometime it will screw up. I bought a DC adapter by mistake, so now i am waiting for my AC adapter to arrive. Testing using batteries now.
Normally when i turn my amp on, there is a loud transient sound. i have no idea if it is considered loud.
So my main issue is my amp works but there are time where it malfunction.
Sometimes when i turn it on, there is a louder than usual transient sound and there will be a constant hum. When i measure my P2 pad, i find that there is 8volts DC output. Measuring my U3,U4 pin 1 and 7 yield the same voltage. Normally when it is function normally, it shows 0Volt (analog signal).
I found that if i switch the amp on realllly slow, it might fix the malfunction. So at the halfway mark, the LED will power on but dimly then turn on fully with a transient sound. Thou its a hit and miss situation so it might not work.
Another thing is, i was testing it using a small speaker, so when the amp was malfunction, i pulled the 3.5mm jack out and measured the voltage across one of my battery and immediately, my speaker started humming softly. Is there emi generated? this only happen when it is malfunctioning.
Normally when i turn my amp on, there is a loud transient sound. i have no idea if it is considered loud.
So my main issue is my amp works but there are time where it malfunction.
Sometimes when i turn it on, there is a louder than usual transient sound and there will be a constant hum. When i measure my P2 pad, i find that there is 8volts DC output. Measuring my U3,U4 pin 1 and 7 yield the same voltage. Normally when it is function normally, it shows 0Volt (analog signal).
I found that if i switch the amp on realllly slow, it might fix the malfunction. So at the halfway mark, the LED will power on but dimly then turn on fully with a transient sound. Thou its a hit and miss situation so it might not work.
Another thing is, i was testing it using a small speaker, so when the amp was malfunction, i pulled the 3.5mm jack out and measured the voltage across one of my battery and immediately, my speaker started humming softly. Is there emi generated? this only happen when it is malfunctioning.
Sometimes the power on/off switch itself might be faulty causing improper +/-9V supply to the opamps resulting 8V DC appearing on o/p. As for humming sound - it might be improper grounding, try some battery operated source like ipod as AC operated source might be creating humming/noise. last but not least chk. for dry solder or best reheat all solder points again.
Regards
availlyrics
Regards
availlyrics
alright, performed the recommended voltage and resistor checks. and it looks alright so far. nothing that is off.
i checked that none of the leads on the bottom side of the board is shorted to the case.
regarding the power switch i thought that might be it, but when i tried to do the current test(with the switch on and properly working), it will "malfunction" again.
this video will shows the issue. Initially its working normally, but the current test is a "100% sure" way to trigger the problem(you can hear the buzz and there is 8volt DC on output). So to fixed it, i have to hold the power button halfway then switch it on fully. i am thinking it is something to do with capacitor. (since holding it halfway discharge it?)
<embed width="440" height="420" type="application/x-shockwave-flash" src="http://v6.tinypic.com/player.swf?file=sfym3n&s=6"><br><font size="1"><a href="http://tinypic.com/player.php?v=sfym3n&s=6">Original Video</a> - More videos at <a href="http://tinypic.com">TinyPic</a></font>
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i checked that none of the leads on the bottom side of the board is shorted to the case.
regarding the power switch i thought that might be it, but when i tried to do the current test(with the switch on and properly working), it will "malfunction" again.
this video will shows the issue. Initially its working normally, but the current test is a "100% sure" way to trigger the problem(you can hear the buzz and there is 8volt DC on output). So to fixed it, i have to hold the power button halfway then switch it on fully. i am thinking it is something to do with capacitor. (since holding it halfway discharge it?)
<embed width="440" height="420" type="application/x-shockwave-flash" src="http://v6.tinypic.com/player.swf?file=sfym3n&s=6"><br><font size="1"><a href="http://tinypic.com/player.php?v=sfym3n&s=6">Original Video</a> - More videos at <a href="http://tinypic.com">TinyPic</a></font>
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See if the second half of this post sounds like what you are experiencing:
http://www.diyaudio.com/forums/head...headphone-amp-diy-project-30.html#post2824139
and this
http://www.diyaudio.com/forums/head...headphone-amp-diy-project-31.html#post2824287
When your O2 is messing up, see if the output voltage is actually climbing up to the 8Vdc from 0Vdc over the course of a second or two as in that second posting (start the amp up with the DMM attached to the output).
If so, the solution might be here, reheating the connections on R12 and R13 even if those solder connections look perfectly OK.
http://www.diyaudio.com/forums/head...headphone-amp-diy-project-31.html#post2825007
http://www.diyaudio.com/forums/head...headphone-amp-diy-project-31.html#post2825111
If those don't make contact then the input bias current of U3 and U4 charges up C13 and C14 to nearly the power supply rail voltage, which in turn puts a large DC voltage on the O2 output due to the unity gain buffer stage. If it is a bad solder connection like that then it would be typical for the problem to come and go.
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opps look like the forum didn't embed the link. Video - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting
mmm and its not quite the same issue. I managed to listen to run it till the battery died. Sounds normal to me. my R12 and R13 measured 40k. which sounds just about right? But i'll try reheating it later.
And the current test is not a "100% sure" way to trigger the problem now ><. cant get it to malfunction. You can see the video i posted. if its not malfunctioning, its working properly.
mmm and its not quite the same issue. I managed to listen to run it till the battery died. Sounds normal to me. my R12 and R13 measured 40k. which sounds just about right? But i'll try reheating it later.
And the current test is not a "100% sure" way to trigger the problem now ><. cant get it to malfunction. You can see the video i posted. if its not malfunctioning, its working properly.
During a time when you are getting 8Vdc on one of the O2 outputs, try measuring the voltages on U3 or U4 (whichever one corresponds to the faulty output) and see what you get on all 8 pins. Measure the voltages between the pins and ground, which is the metal shell of the gain switch.
NOTE: 8Vdc on the O2 output is enough to damage headphones! You may want to leave your headphones unplugged until that one gets fixed.
OK, pin 4 at 1.73Vdc to ground is probably the bad guy. That is your negative power supply rail, and should be around the negative value of whatever is on pin 8 to ground, so somewhere around -8.48Vdc. Without having their proper negative supply rail voltages, U3 and U4 are just doing the best they can with the rest of those voltages. If you can, when the O2 is messing up, also measure the voltages on U2 pins 4 and 8, both with respect to ground (gain switch shell).
So... I would guess bad negative mosfet (Q2) and/or a bad U2, assuming that U2 pins 4 and 8 measure with proper power supply rail voltages. There have been posts in the big O2 thread where people with loud turn on or turn off transients solved them by replacing either or both of those (Q2 and U2). In the comments on RocketScientist's site for the O2 he states at one point that bad mosfet(s) can turn on or off too slowly, creating the pops.
If you decide to try replacing them, and have to order parts, probably good to order both Q1 and Q2 along with a U2 to have on hand for troubleshooting.
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That can also be the sign of a bad U2 or mosfet - or bad solder joint. Sounds like your meter hooked to the circuit is causing the negative rail part of the power management circuit to toggle from off to on.
It couldn't hurt to try re-heating all the solder joints in the power management circuit. U2, both mosfets, R8, C21, R6, R25, the LED, and all the other resistors and capacitors in that area. Just another 1 second or so with the soldering iron on each.
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Noise injection from the test leads, if just the right conditions occur. If Q2 doesn't solve it, do try U2 also. A couple of cases of bad U2s have caused similar things. Good luck!
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